What does "mocking" mean in E2E tests?

Mocking in E2E tests is substituting real external requests and responses (usually network ones) with pre-prepared fake data, so the test runs predictably and stably.

#Why it is used

• eliminate dependency on the real backend, network and delays
• reproduce the same behavior on every run
• test scenarios that are hard or slow to get from the real API (errors, special states, etc.)

#What this looks like, essentially

• the test sends a request → a fake response is substituted instead of the real server
• the UI receives the data and behaves as if it were interacting with the real system

#What is mocked most often

• fetch / XHR
• API responses (JSON)
• server errors
• delays and statuses (200, 400, 500, timeout)

The key idea: a mock does not test the real backend, it captures the frontend's behavior under controlled conditions.